Shanti Institute of Technology, Meerut (U.P.) - 250501, India

122 International Journal of Scientific Research Engineering & Technology (IJSRET) ISSN: 2278–0882

EATHD-2015 Conference Proceeding, 14-15 March, 2015

3- COIL STARTER USE FOR STARTING D.C MOTOR

Rohit Kumar

Lecturer, Electrical Engineering Department

S.I.T. Meerut

ABSTRACT

We know that D.C. motor is self starting. But we use

the external method for starting to D.C motor for

safety purpose. Because if we are not use starter then

motor can be burn. I shall explain further in this paper

why burn motor if we will not use starter. Today we

are using 3- point starter & 4-point starter. 4-point

starter remove the drawback of 3-point starter. But 4-

point starter having also some draw back. This draw

back can be modifying by using 3- coil starter. Which

will explain in this paper? The 3- coil starter has a lot

of constructional and functional similar4- point starter,

but this special device has an additional coil in its

construction, which naturally brings about some

difference in its functionality, though the basic

operational characteristic remains the same.

I. INTRODUCTION D.C motor is self staring motor. But several methods

are used for starting to D.C. motor. In present time in

industry. These two method are used in industry .these

are given as 3-point starter & 4- point starter .Now in

this research paper modified these starter draw Back.

This starter is known as 3- coil starter. This starter is

basically modified 4-point

Starter drawback.

II. STARTING OF DC MOTOR The starting of DC motor is somewhat different from

the starting of all other types of electrical motors. This

difference is credited to the fact that a dc motor unlike

other types of motor has a very high starting current

that has the potential of damaging the internal circuit

of the armature winding of dc motor if not restricted to

some limited value. This limitation to the starting

current of dc motor is brought about by means of the

starter. Thus the distinguishing fact about the starting

methods of dc motor is that it is facilitated by means of

a starter. Or rather a device containing a variable

resistance connected in series to the armature winding

so as to limit the starting current of dc motor to a

desired optimum value taking into consideration the

safety aspect of the motor.

Now the immediate question in why the DC motor

has such high starting current? To give an

explanation to the above mentioned question let us

take into consideration the basic operational voltage

equation of the dc motor given by,

E = IaRa + Eb

Where E is the supply voltage, Ia is the armature

current, Ra is the armature resistance. And the back

emf is given by Eb.

Now the back emf, in case of a dc motor, is very

similar to the generated emf of a dc generator as it‟s

produced by the rotational motion of the current

carrying armature conductor in presence of the field.

This back emf of dc motor is given by

and has a major role to play in case of the starting of

dc motor.

From this equation we can see that Eb is directly

proportional to the speed N of the motor. Now since at

starting N = 0, Eb is also zero, and under this

circumstance the voltage equation is modified to

E=Ia Ra +0

For all practical practices to obtain optimum operation

of the motor the armature resistance is kept very small

usually of the order of 0.5 Ω and the bare minimum

supply voltage being 220 volts. Even under these

circumstance the starting current, Ia is as high as

220/0.5 amp = 440 amp.

Such high starting current of dc motor creates two

major problems.

1) Firstly, current of the order of 400 A has the

potential of damaging the internal circuit of the

armature winding of dc motor at the very onset.

2) Secondly, since the torque equation of dc motor is

given by

T ∝ ф Ia

Shanti Institute of Technology, Meerut (U.P.) - 250501, India

123 International Journal of Scientific Research Engineering & Technology (IJSRET) ISSN: 2278–0882

EATHD-2015 Conference Proceeding, 14-15 March, 2015

Very high electromagnetic starting torque of DC

motor is produced by virtue of the high starting

current, which has the potential of producing huge

centrifugal force capable of flying off the rotor

winding from the slots.

Method use starting D.C. motor

I) 3-point starter

II) 4-pont starter

New method explain in this research paper

I) 3-coil starter

III. 4 point starter

Constructional Details of 4-point starter

A 4 point starter is mainly the no-volt release coil is

connected directly across the supply line through a

protective resistance R to limit the starting current to a

certain safer range. The resistance is subdivided in

many variable resistances and this section of resistance

contains the contact points called Studs, which are

calibrated separately from OFF, 1, 2, 3, 4, 5 …. ,RUN.

The main reason behind the name of 4 point starter is

the 4 main points of the starter which are as follows:

Line Terminal „L‟, which is to be connected to

the positive of supply.

Field Terminal „F‟, which is to be connected to

the field winding.

Armature Terminal „A‟, which is to be

connected to the armature winding.

A 4th point N which is to be connected to the

No Voltage Coil (NVC).

Now we are going to discuss about the constructional

details of this 4 point starter, how this each and

every parts are interconnected and also the sub-

elements or subparts used in the construction of this 4

point starter. With respect to the figure, the only

difference between a three point starter and a four-

point starter is the manner in which no-volt release coil

is connected. However, we can tell that the working of

the two starters is the same. The basic difference

between three point and four pint starter is the

connection of NVC. In 3 point starter, NVC is in series

with the field winding while in four point starter NVC

is connected independently across the supply through

the fourth terminal called „N‟ in addition to the „L‟, „F‟

and „A‟. Therefore we can say any change in the field

current does not affect the performance of the NVC.

Thus it is ensured that NVC always produce a force

which is enough to hold the handle in „RUN‟ position,

against force of the spring, under all the operating

conditions. Such a current is adjusted through NVC

with the help of fixed resistance R connected in series

with the NVC using fourth point „N‟.

Working principle of 4-point starter

As we provide the d.c. supply to the motor, to make it

switch on, the handle starts moving against the spring

force to make a contact with stud No. 1, which was

initially at OFF position. Thus field winding gets

supply through the parallel path provided to starting

resistance with the help of NVC. This is how we see

the entire starting resistance comes in series with the

armature and armature current which is high initially,

gets checked to certain limit. Similar way the handle

starts moving towards the other studs 2, 3, 4 etc., thus

reducing the starting resistance gradually from the

armature circuit and reaches the RUN position making

the starting resistance R equal to zero and the motor

keeps on rotating at its normal speed. Thus the

working of the 4 point starter is just same as the 3

point starter. But we can say the main difference

between a 3-point starter and a 4-point starter is the

manner in which no-volt release coil is connected. The

three-point starter also provides protection against an

open-field circuit which is not at all provided by the

four-point starter.

What is the main disadvantage of 4-point starter?

We have seen the only limitation of the four point

starter is that it does not provide high speed protection

to the motor. Under running condition, field gets

opened then the field current reduces to zero. But there

is some residual flux remaining and N ∝ 1/Φ the motor

tries to run with dangerously high speed. This is called

high speeding action of the motor. Thus we see in four

point starter NVC is connected directly across the

supply and its current is maintained irrespective of the

current through the field winding. So it will always

maintain the handle in the run position, as long as

supply is provided. And thus it does not protect the

motor from field failure conditions which result into

the high speeding of the motor. The most important

difference between a three-point starter and a four-

point starter is the manner in which no-volt release

coil is connected. The three-point starter also provides

protection against an open-field circuit which is not at

all provided by the four point starter.

Shanti Institute of Technology, Meerut (U.P.) - 250501, India

124 International Journal of Scientific Research Engineering & Technology (IJSRET) ISSN: 2278–0882

EATHD-2015 Conference Proceeding, 14-15 March, 2015

IV. 3-COIL STARTER

Construction details of 3-coil starter-

3-coil starter is also similar to 4- point starter but

having several difference in construction.

It, s explains as:

It has three coils. These explain as:

I) OLC (OVER LOAD COIL)

II) NVC(NO VOLTAGE COIL)

III) OCC(OPEN CIRCUIT COIL)

These are following resistance R1, R2, R3, R4 extra

resistance connected in series with armature in staring

of D.C. motor. OCC (open circuit coil) connected

across the field winding of the motor. Field winding

terminals F1F2. Terminal f1 is connected to NVC (no

voltage coil). Armature terminals A1A2. A1 is

connected to the last resistance terminals. Terminals

a1a2 will become short circuit across the NVC coil.

Terminal a1a2 will become short circuit when OLC coil

operated. Terminals b1b2 will become short circuit coil

across the NVC coil when OCC coil operated.

Working of 3-coil starter-

As we provide the D.C. supply to the motor, to make

it switch on, the handle starts moving against the

spring force to make a contact with stud No. 1, which

was initially at OFF position. Thus field winding gets

energies by passing the current. Field winding

connected in parallel across the OCC coil. Total

supply current is not passing through the field winding

because a parallel resistance connected across the field

winding. But this resistance having a very high value.

This is how we see the entire starting resistance comes

in series with the armature and armature current which

is high initially, gets checked to certain limit. Similar

way the handle starts moving towards the other studs

2, 3, 4 etc., thus reducing the starting resistance

gradually from the armature circuit and reaches the

RUN position making the starting resistance R equal to

zero and the motor keeps on rotating at its normal

speed. Thus the working of the 3- coil starter is just

same as the 4 point starter.

V. Difference between 3-coil starter & 4-

point starter 3- Coil starter remove the problem of 3- point starter &

4-point starter. Drawback in 4- point starter is that if

field winding becomes open circuit then speed of dc

motor become very high. 3- Coil starter remove this

drawback of 4- point starter. When field winding will

open circuit the total supply current pass through the

OCC coil. So that OCC coil will energies. Due to

energies of coil OCC terminal b1b2 become short

circuit across the NVC coil. So that no current flow

through the NVC coil. Then NVC coil deaneries due

this reason handle will back to OFF position. If the

short circuit occurs across the field winding then very

high current flow through the field winding. Due to

this high current OLC coil energies. Due to energies

OCC terminal a1a2 short circuit. When a1a2 short circuit

no current flow through the NVC coil and handle will

become to back OFF position.

S.N POINT

STARTER

3- COIL TARTER

1 point starter

having 2 coil

3-coil starter having 3 coil

2 these are

following coil

in 4-point

starter. I) OLC

II) NVC

These are following coil in 3-

coil starter

I)OLC II) NVC III) OCC

3 Drawback in 4-

poin Draw

back of 4-point

starter. Is

that it fail in

the case of

open circuit in

field winding

that

3-coil starter is operated in the

case of Open circuit of field

winding. It modify the draw

back of 4- point starter.

VI. CONCLUSION

After study this research paper. I finalize that with the

help of 3- coil starter we can remove the drawback of

3- coil starter. With the help of 3-coil starter D.C

motor will become reach `

In off state if the field winding opens. So that motor

not runs very high speed in the case of open field

winding. I will try to that it will practically possible or

not in lab. If this theory successful then we can solve a

very big drawback of 4-point starter.

REFERANCE [1] Dr.P.S.Bimbhra “Generalized theory of electrical

machines” Khanna Publishers, Fifth edition, 22nd

Reprint , 2012

[2] Dr.P.S.Bimbhra “Electrical Machinery” Khanna

Publishers, Seventh edition , 23rd

edition 2012

[3] Ashfaq husain “Electrical machine” Dhanpat Rai &

co., Second edition, Reprint , 2010

[4] Web site “electrical4u.com